1. Field of the Invention
The present invention concerns an air driver device used for tightening screw members such as screws, bolts & nuts, etc., more specifically an air driver device for tightening screw members at a prescribed tightening force.
2. Background of the Related Art
Conventionally, an air driver device is used for tightening screw members such as screws, bolts & nuts, etc., and is put to practical use by tightening screw members at a prescribed tightening force, by shutting off a supply of compressed air to an air motor, by means of a tightening torque control mechanism and a shut-off valve mechanism, in a case where the tightening torque has reached a set torque value (refer to JP 58-34265 B, JP 2004-106146 A).
This conventional air driver device comprises an operating shaft for turning an air motor by opening the shut-off valve of a shut-off valve mechanism disposed in the air supply channel by inwardly pushing a spindle, and is designed in such a way as to connect a cam turned by the air motor with the spindle, by means of a torque control mechanism which makes a differential rotational motion, relatively, in a case where the tightening torque has reached the set torque value, so as to stop the air motor by closing the shut-off valve of the shut-off valve mechanism by moving the push rod with a differential rotational motion of the torque control mechanism.
To be more concrete, as a torque control mechanism, this air driver device is designed to put balls 126, which are fit and supported in ball fitting holes 121 drilled in the spindle 101, in contact with the respective ball supporting faces 120 of the cam 105, and slidably fit, on the outer circumference of the ball fitting & supporting portion of the spindle 101, a cam ring 123 tapered on the face to be in contact with the balls 126, in the axial direction, to transmit the rotational driving force from the cam 105 turning with the air motor 103, through the balls 126, to the spindle 101, as shown in FIG. 13˜FIG. 14. On the other hand, this air driver device adopts a construction in which, when the tightening torque reaches the set torque value, the balls 126 are pushed outwardly, in the direction of the outer circumference, from the ball supporting faces 120 of the cam 105 in order to stop the transmission of torque between the cam 105 and the spindle 101. In the case where the balls 126 are pushed upwardly in the direction of outer circumference, from the ball supporting faces 120 of the cam 105, a differential motion in the direction of rotation is produced between the cam 105 and the spindle 101, producing a difference of rotation between the two. This causes a pilot pin 122, which turns together with the cam 105, to turn relatively against the spindle 101, to push up a lock pin 140 with the projected side of its chamfered step portion 131, release the engagement between the pilot pin 122 and the chamfered step portion 131 by the lock pin 140 and enable movement of the pilot pin 122 and the push rod 104, so as to stop the air motor by closing the shut-off valve 110 of the shut-off valve mechanism.
As explained above, the above-mentioned conventional air driver device, which uses, as a torque control mechanism, a mechanism of complicated structure composed of constituent members such as a cam 105, balls 126, a cam ring 123, etc., is difficult to realize in compact size, and also presents a problem that the constituent members are easily worn and lack durability.